Wireless local area networks (WLANs) have seen explosive growth in recent years as a last-hop connectivity solution. Such networks, which typically operate in accordance with IEEE 802.11-type protocols, often operate in the 2.4 and 5 GHz bands where unlicensed spectrum is very limited. Due to the growth in usage of WLANs, network administrators are faced with an emerging challenge of efficiently managing bandwidth resources to provide better service to clients.
WLANs typically are implemented through the use of one or more access point (APs) that serve as gateways for one or more clients, which can include, for example, wirelessly-equipped laptop or notebook computers. Whenever a given client is in communication with a given AP, the communication takes place by way of a given communication frequency channel. All communication between an AP and its associated clients (which form a Basic Service Set (BSS)) occur in the channel assigned to the AP.
Given that APs are communicating via respective communication channels, clients establish communication with the APs of their choice by selecting the appropriate channels associated with those APs. Often a client simply selects a channel by scanning the wireless medium for a strong signal (or the strongest signal) from an AP, and then selects that channel of the AP for its communications.
Channel assignment in conventional WLANs is determined by the APs based upon various measured information available to those APs, and/or as specified by an administrator. The manner of channel assignment used for WLANs differs from that employed in other domains, since those other manners of channel assignment typically are not applicable for WLANs. For example, channel assignment for cellular networks is traditionally modeled as a vertex coloring problem. However, the irregular coverage topologies present in WLANs due to the vagaries of the indoor radio frequency (RF) environment make such channel assignment algorithms inefficient when applied to WLANs.
Instead, as a basic design rule in assigning channels for WLANs, APs within range of one other are set to different “non-overlapping” channels. Further, multiple techniques are often employed to assign channels to APs to reduce interference between them. For example, network administrators often perform detailed Radio Frequency (RF) site surveys, often using spectrum analyzers, prior to setting up APs within a building and use this information to assign specific channels to the APs. Also, subsequent to the initial channel assignments, each AP continuously monitors its assigned channel for data transmissions by other APs and their clients. If the volume of traffic in that channel (from other APs or clients of other APs) is greater than a threshold, the first AP moves to a less congested channel, a technique that can be referred to as “Least Congested Channel Search” (LCCS).
Although conventional channel assignment techniques such as the LCCS technique do achieve workable channel assignments, such conventional channel assignment techniques often do not result in channel assignments that produce optimal bandwidth usage. The LCCS technique in particular is unable account for circumstances in which, while there is not significant interference between neighboring APs, there is nevertheless interference occurring (or potentially occurring) between APs and clients of neighboring APs, or between the clients of neighboring APs. This inability to account for the “hidden interference” occurring due to the presence of clients limits the degree to which available bandwidth can be efficiently used. Indeed, clients that are in conflict can suffer from drastic reduction in throughput. In particular, the reduction factor experienced by a given client can be non-linear in the total number of stations (clients or APs) in conflict with the given client.
In addition to being unable to account for such hidden interference, conventional channel assignment techniques such as the LCCS technique do not at all address issues of load balancing among different APs. That is, channel assignment is accomplished without any consideration of how many clients may or will be in communication with each given AP. Although in at least some circumstances, load balancing issues are considered independently of channel assignments, the lack of joint consideration of load balancing issues in conjunction with channel assignment issues also limits the degree to which available bandwidth can be efficiently used.
For at least the above reasons, therefore, it would be advantageous if an improved method and/or system for assigning channels to APs in WLANs could be developed. More particularly, it would be advantageous if, in at least some embodiments, such an improved method and/or system enabled the assignment of channels to APs so that enhanced bandwidth usage (and enhancements in overall throughput) could be achieved by the WLANs. Further, in at least some embodiments, it would be advantageous if such an improved method and/or system was able to account for interference (e.g., “hidden interference”) that cannot be taken into account by conventional channel assignment techniques, and/or was able to address load balancing issues in conjunction with the process of assigning channels to APs.